Heat transfer fluids ideally should be operable at a broad range of temperatures, have low viscosities to minimize pumping problems at low temperatures and provide an acceptable rate of heat transfer, have a sufficiently low freezing point, decompose only at slow rates in use, and resist the formation of degradation products that foul the systems in which they are used. Moreover, for convenient handling, clean up and disposal, it is desirable that they be environmentally non-hazardous and of low toxicity.
Several classes of heat transfer fluid compositions are well known and utilized commercially, all of which satisfy at least some of the criteria listed above. Exemplary of some of these are petroleum oils, synthetic aromatic compounds such as alkylated aromatics, phenylene oxides and diphenylene oxides, terphenyls, phenoxybiphenyls and phenoxyterphenyls, polyalkylene ether glycol type copolymers of ethylene oxide and propylene oxide, and polydimethylsiloxane based silicone fluids. All of these materials have a common disadvantage in being petroleum based and thus subject to environmental restrictions and increasing prices as the supply of petroleum diminishes.
Density, thermal conductivity, specific heat and kinematic viscosity are specific parameters that describe the performance of a heat transfer medium. Other factors such as environmental impact, toxicity, flammability, and corrosive nature can also affect the feasibility and performance of a heat transfer medium. Furthermore, the freezing and boiling points, and thermal and oxidative stability of the heat transfer fluids, restrict the operational temperature range of the heat transfer processes in which they are used.
It would be a substantial advantage if heat transfer fluids were available that were made from materials that are derived from renewable biological resources and can be used as base fluids in formulations for high operating temperatures where traditional glycols have limited use due to their volatility and poor thermal stability.